1. Field of the Invention
This invention relates to a magnetoresistive head for use in a magnetic disk apparatus, video tape recorders (VTRs), or the like, and a magnetic write/read apparatus incorporating a magnetoresistive head. More particularly, the invention relates to a magnetoresistive head which generates little Barkhausen noise, which has high sensitivity and high linear recording resolution, and which can read signals of a high S/N ratio, and to a magnetic write/read apparatus which comprises this magnetoresistive head.
2. Description of the Related Art
A magnetoresistive head (hereinafter referred to as "MR head") is attracting much attention as a next-generation reading head to replace the conventional inductive magnetic head. Among the various types of MR heads hitherto known is a shield type MR head. The shield type MR head comprises an MR element, a shield layer having high magnetic permeability, and an insulating film interposed between the element and the shield layer. It is difficult to reduce the thickness of the insulating film to a value less than a particular one. Were the film too thin, sufficient insulation between the element and the shield layer could no longer be maintained. It is therefore hard to improve the linear recording resolution of the shield type MR head.
To solve this problem, a so-called dual-element type MR head has been developed as is disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 53-37204. A dual-element type MR head has a multilayer structure; it comprises two anisotropy magnetoresistive (MR) elements and an intermediate layer interposed between the elements. The intermediate layer is either a nonmagnetic insulating layer or a nonmagnetic metal layer.
The MR elements apply operation-point biases of opposite polarities in a direction perpendicular to the plane of a magnetic recording medium when sense currents of the same polarity flow through both elements in a widthwise direction of the recording tracks of the medium. Therefore, the two MR elements change in resistance in the opposite directions when exposed to signal magnetic fields of the same polarity. The resistance change in one MR element cancels out the resistance change in the other MR element. As a result, the dual-element MR head generates no output. Conversely, when the elements are exposed to signal magnetic fields of the opposite polarities, their resistances change in the same polarity. In this case, the resistances of the MR elements strengthen each other, whereby the dual-element MR head generates an output.
As may be understood from the preceding paragraph, the dual-element MR head is a reading head which performs a so-called differential operation to generate signals. Since the thickness of the intermediate layer determines the linear recording resolution, this MR head need not have a shield layer, and is therefore simple in structure. The dual-element MR head can read signals of a high S/N ratio and have high linear recording resolution, as is known in the art.
However, no techniques have been devised which can apply an effective exchange bias field to the pair of MR elements, to thereby suppress Barkhausen noise, without compounding the structure of the dual-element MR head. The dual-element MR head has yet to be reduced to practice. Thus, there has been a demand for some means which would render the dual-element MR head practical.
Recently it has been found that a multilayer film, such as a spin-valve film, which comprises two magnetic films and a nonmagnetic film interposed between the magnetic films, exhibits large magnetoresistive far more sensitive than the anisotropy magnetoresistive conventionally attained. Research is being made for the possibility of incorporating MR elements with such an enormous magnetoresistance effect, into reading heads. Nevertheless, no MR reading head has ever known which can perform a differential operation with high reliability, to reproduce signals of a high S/N ratio at high linear recording resolution.